Acceleration of real time computer vision processing on UAVs through GPS attitude estimation

ABSTRACT

A method for applying GPS UAV attitude estimation to accelerate computer vision. The UAV has a plurality of GPS receivers mounted at fixed locations on the UAV. The method includes receiving GPS signals from each GPS satellite in view of the UAV, the GPS measurements comprising pseudo-range and carrier phase data representing the distance between each GPS receiver and each GPS satellite. Carrier phase and pseudo-range measurements are determined for each GPS receiver based on the pseudo-range and carrier phase data. The GPS carrier phase and pseudo-range measurements are compared pair-wise for each pair of GPS receiver and satellite. An attitude of the UAV is determined based on the relative distance measurements. A 3D camera pose rotation matrix is determined based on the attitude of the UAV. Computer vision image search computations are performed for analyzing the image data received from the UAV in real time using the 3D camera pose rotation matrix.

BACKGROUND

This disclosure relates to computer vision on an unmanned autonomousvehicle (UAV) and more particularly to determining camera pose rotationbased on the attitude of the UAV for computer vision.

There is much excitement and hype, surrounding technology for unmannedaerial vehicles (UAV), commonly known as UAVs. Despite ample progress,several substantial technical challenges yet remain before “ubiquitousUAVs” becomes a realistic vision of the future. One core,well-established challenge is in enabling UAVs to engage seamlessly withtheir environment. Addressing this challenge seems to demand amplecomputer vision, and in real time.

We are considering the need for computer vision on small flyingUAVs/unmanned autonomous vehicles (UAVs). We believe computer visionwill become increasingly essential for engaging with humans, foroperating in unknown environments, for spotting targets to find orfollow from a distance, for comprehending and responding to the visualor multispectral data they collect in real time, for collaborating withother UAVs or robots, and for finding means to recharge or refuel. Giventhese visual needs, capabilities for real time computer vision on UAVplatforms seem like a must. Further, as these functions may often besafety critical, it may not be wise to offload to powerful back-endcloud compute systems. Much like a self-driving car, UAVs must also bemostly self-sufficient in their compute needs. However, unlike aself-driving car, the constraints in form factor, weight, and energy inthe compute platform are highly constrained. Flying with a smalllow-power system on a chip (SoC) like the Raspberry Pi is quitefeasible. However, a high performance server with GPUs is not currentlyrealistic. Indeed, the resource constraints endemic to mobile computingon smartphones again apply to mobile computing on UAVs.

However, computer vision heuristics are often heavy weight, anddifficult to run in a computing platform that can fit in the weight andform factor limitations of most UAVs. Several prior works consider meansfor precise relative GPS tracking; GPS applied to “attitude”(orientation) estimation, especially in the context of airplanes,satellites, and ships; and the use of GPS “position” in computer vision.However, these techniques are very time consuming and therefore arefeasible for obtaining real time data.

SUMMARY

In one embodiment, a method for applying GPS UAV attitude estimation toaccelerate computer vision is disclosed. The UAV has a plurality of GPSreceivers mounted at fixed locations on the UAV. The method includesreceiving GPS signals from each GPS satellite in view of the UAV, theGPS signals comprising pseudo-range and carrier phase data representingthe distance between each GPS receiver fixed to the UAV and each GPSsatellite in view of the UAV. Carrier phase and pseudo-rangemeasurements are determined for each GPS receiver fixed to the UAV basedon the obtained pseudo-range and carrier phase data. Te GPS carrierphase and pseudo-range measurements are compared pair-wise for each pairof GPS receiver and satellite. An attitude of the UAV is determinedbased on the relative distance measurements. A 3D camera pose rotationmatrix is determined based on the attitude of the UAV. Image data from acamera mounted on the UAV is received and computer vision image searchcomputations are performed for analyzing the image data received fromthe UAV in real time using the 3D camera pose rotation matrix.

In one embodiment, determining the carrier phase and pseudo-rangemeasurements includes estimating an integral component of the distancebetween each GPS receiver and each GPS satellite using the pseudo-rangedata and estimating a fractional component of the distance between eachGPS receiver and each GPS satellite using the carrier phase data. In oneembodiment, comparing the GPS carrier phase and pseudo-rangemeasurements includes comparing the pseudo-range and carrier phaseestimated distance components pair-wise between the GPS receiver andsatellite pairs. In a further embodiment, determining an attitude of theUAV includes calculating relative distances between the GPS receiversand each satellite based on the comparisons and determining the attitudeof the UAV based on the relative distances between GPS receivers andsatellites.

In another embodiment, determining a 3D camera pose rotation matrixincludes determining a first attitude of the UAV at a first time point,determining a second attitude of the UAV at a second time point,encoding the first attitude of the UAV as a first 3×3 rotation matrixand encoding the second attitude of the UAV as a second 3×3 rotationmatrix; and calculating a rotation of the camera between the first andsecond time points by multiplying first rotation matrix by the inverseof the second rotation matrix and encoding the results as the 3D camerapose rotation matrix.

A further embodiment includes locating coordinates of an imagecorresponding to the first and second time points in a first video orphotograph stream time-synchronized to the raw GPS measurements,obtaining a camera matrix defining properties of the camera, combiningthe camera matrix and the 3D camera pose rotation matrix to determinepredicted coordinates of the image in a second video or photographstream time, projecting the predicted coordinates of the image into thesecond video or photograph stream time and using the projectedcoordinates as a starting point for a search in the second video orphotograph stream for an image having the same physical characteristicsof the image.

In one embodiment, a non-transitory article of manufacture tangiblyembodying computer readable instructions, which when implemented, causesa computer to perform the steps of a method for applying GPS UAVattitude estimation to accelerate computer vision, the UAV having aplurality of GPS receivers mounted at fixed locations on the UAV. Thesteps include receiving raw GPS measurements from each GPS satellite inview of the UAV, the raw GPS measurements comprising pseudo-range andcarrier phase data representing the distance between each GPS receiverfixed to the UAV and each GPS satellite in view of the UAV, determiningcarrier phase and pseudo-range measurements for each GPS receiver fixedto the UAV based on the obtained pseudo-range and carrier phase data,comparing the GPS carrier phase and pseudo-range measurements pair-wisefor each pair of GPS receiver fixed to the UAV and GPS satellite in viewof the UAV to determine relative distance measurements, determining anattitude of the UAV based on the relative distance measurements,determining a 3D camera pose rotation matrix based on the attitude ofthe UAV, receiving image data from a camera mounted on the UAV andperforming computer vision image search computations for analyzing theimage data received from the UAV in real time using the 3D camera poserotation matrix.

In one embodiment, a computer system for applying GPS UAV attitudeestimation to accelerate computer vision, the UAV having a plurality ofGPS receivers mounted at fixed locations on the UAV, includes one ormore computer processors, one or more non-transitory computer-readablestorage media, and program instructions, stored on the one or morenon-transitory computer-readable storage media, which when implementedby the one or more processors, causes the computer system to perform thesteps of receiving raw GPS measurements from each GPS satellite in viewof the UAV, the raw GPS measurements comprising pseudo-range and carrierphase data representing the distance between each GPS receiver fixed tothe UAV and each GPS satellite in view of the UAV, determining carrierphase and pseudo-range measurements for each GPS receiver fixed to theUAV based on the obtained pseudo-range and carrier phase data, comparingthe GPS carrier phase and pseudo-range measurements pair-wise for eachpair of GPS receiver fixed to the UAV and GPS satellite in view of theUAV to determine relative distance measurements, determining an attitudeof the UAV based on the relative distance measurements, determining a 3Dcamera pose rotation matrix based on the attitude of the UAV, receivingimage data from a camera mounted on the UAV and performing computervision image search computations for analyzing the image data receivedfrom the UAV in real time using the 3D camera pose rotation matrix.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention willbecome apparent from the following detailed description of illustrativeembodiments thereof, which is to be read in connection with theaccompanying drawings, in which:

FIG. 1 is a schematic of a UAV having a series of GPS receivers mountedto the arms of the UAV.

FIG. 2 is a flow chart of one embodiment of the method applying GPS UAVattitude estimation to accelerate computer vision.

FIG. 3 is a flow chart of one embodiment of the method for determiningcarrier phase and pseudo-range measurements and determining the attitudeof the UA.

FIG. 4 is a flow chart of one embodiment of determining a 3D camera poserotation matrix.

FIG. 5 is a flow chart of using the camera pose rotation matrix toaccelerate computer vision.

FIG. 6 is a block diagram of an exemplary computing system suitable forimplementation of this invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

This disclosure is directed to shortcuts to computer vision, based onprecision motion sensing. In particular, the disclosure is directed tothe use of multiple GPS receivers to estimate UAV 3D orientation, moreprecisely than is possible through inertial sensing. In one embodimentapplied to computer vision, an order of magnitude reduction in thesearch space of spatial computer vision heuristics is achieved.

In one embodiment, GPS attitude estimation is applied to acceleratecomputer vision. While the disclosure has applications to UAVs, broaderuse cases would also apply, for example, automotive applications (e.g.,self-driving cars).

In one embodiment, precise sensory assistance for computer vision caneliminate computer vision variables. Substituting known terms for theunknown can reduce the search space an order of magnitude. Specifically,a primary unknown in several key computer vision heuristics is often therelative camera pose across two or more successive images. Spatialheuristics such as structure from motion (SfM) requires spatiallylinking these images. For example, the system must deduce severalkey-points in image A that correspond to the same points in physicalspace found in image B. If it is known that images A and B were actuallytaken from a fixed point P with a known rotation angle APB in between,the problem immediately becomes far easier because the system canre-project A based on the angle APB. Key points in B are likely toappear nearby the re-projected points from A. Importantly, they will notappear precisely at the re-projected point, due to the 3D structurecaptured in A and B. However, image changes strictly due to camera poseare eliminated and the search space is commensurately reduced.

From the above example, it should be clear that computer visioncomputations can be accelerated through sensory inputs. Thus, thequestion becomes how to estimate the relative camera pose across aseries of images. Of course, UAVs can and do feature a gamut of spatialand inertial sensors: GPS, compass, barometer, accelerometer, andgyroscope. While these can be applied, high precision id needed. Ifsensory estimates contain too much error, the efficacy of computervision heuristics will be intolerably degraded.

Camera pose can be decomposed into two parts: position and orientation.For relative pose (the delta between two images from the same camera),these become rotation (e.g., APB) and translation—how much the camerahas rotated and moved. In the context of UAVs, which generally fly inopen outdoor spaces, GPS presents an obvious opportunity to estimatetranslation well. Differential GPS (DGPS) has been applied to estimaterelative motion at centimeter scale (i.e., using a secondary fixed GPSon the ground to compensate for transmission delays in the ionosphere).Further, given that subjects in view of a UAV are likely far away, a fewcentimeters of error would translate to very little difference in theresultant image. Thus, at great distance, computer vision is translationinsensitive, and DGPS is well suited for translation estimation.However, at all scales, computer vision is certainly rotation sensitive.

However, in the context of UAVs, accurate rotation measurement becomesdifficult. Due to their small, high torque DC motors, UAVs can changedirection rapidly. Compared to aviation, the nature of quad-copterflight may be aggressive in ways that would make humans ill.Accelerometers and gyroscopes are also subject to these inertial forces,and may track relative rotational positions poorly under angularacceleration. For applications to computer vision, absolute measurementsare more promising than inertial dead reckoning.

Absolute rotational tracking requires a well known point of reference.One possibility is through computer vision—tracking the ground—asnaturally occurs when structure from motion is applied on UAV imagery.However, there are advantages to reducing the quantity of computervision computation. Possible approaches, such as structure from motion,are themselves complex: using computer vision to speed itself does notseem promising.

In certain contexts, GPS has been applied to estimate absoluteorientation—or “attitude” in aeronautical terms. In spacecraft, onairplanes, and on ships, GPS receivers can be spread far apart at knowndistances. Relative distances between each receiver and GPS satellitescan be applied to infer angular position. Especially, more complex GPScalculations based on the carrier phase measurement can make theserelative measurements extremely precise.

As shown in FIG. 1 , several GPS receivers, are mounted to a UAV orother vehicle 10. In the exemplary embodiment in FIG. 1 , four receivers12 are mounted to four UAV arms 14, each connected to UAV body 16. GPSreceivers 12 are physically mounted to the arms 14 of the UAV craft 10.The distances between GPS receivers 12 are precisely measured. In oneembodiment, the receivers 12 are positioned to maximize the distancebetween the receivers, which increases the length of computationalbaselines, and ultimately enhancing attitude estimation accuracy. In theembodiment shown in FIG. 1 , the receiver-to-receiver distances are 26cm distance on short side of UAV craft 10, and 38 cm distance on thelong side of UAV craft 10. In one embodiment, the GPS receivers 12 aremounted on same plane for measurement accuracy. In this disclosure, aGPS receiver can be a GPS antenna or a full receiver.

FIG. 2 shows one embodiment of the method for applying GPS attitudeestimation to accelerate computer vision. In step S20 the receiversreceive raw GPS measurements for each satellite in view. In step S23 thesystem determines carrier phase and pseudo-range measurements. In stepS24 the system compares pair-wise the GPS carrier phase and pseudo-rangemeasurements. In step S26 the system determines an attitude of the UAVbased on relative distance measurements. In step S28 the systemdetermines a 3D camera pose rotation matrix based on the attitude of theUAV. In step S30 the system performs computer vision image search usingthe camera pose rotation.

In step S20, the GPS hardware devices provide the raw data representingthe distance between the receiver and satellite. Each are provided fromthe GPS hardware by USB, serial, wireless RF or other communicationmechanism to a computer. These distances are composed of two parts, anintegral component—estimated as a pseudo-range distance—and a fractionalpart—estimated by the carrier phase. The phase is a fractional value[0, 1) of a wavelength.

In step S23 GPS carrier phase measurements at each GPS receiver areobtained by multiplying the fractional phase by the wavelength length(e.g., in meters), to obtain a distance as a fraction of a wavelength.Combining the integral and fractional components results in a precisedistance between receiver and satellite. The availability of thefractional component gives very high accuracy with granularity in theorder of centimeters while granularity of pseudo-ranges is in the orderof 30 cm (i.e., one wavelength at GPS RF frequencies).

These measurements are determined for every GPS receiver 12, for everysatellite. From all measurements taken together, a precise geometry ofhow the receivers, in fixed relative positions on the UAV 10, relate tothe reference GPS satellites is obtained. However, these measurementswill have substantial error—and cannot be directly used. Instead, acomparison of the distance measurements pair-wise between receivers andsatellites is made. The results is relative pseudo-ranges and relativecarrier phases. Differences among carrier phase will be highlyprecise—especially, as several sources of GPS error will cancel in thecomparison (e.g., correlated clock errors). These relative measurementsprovide a geometry of the relative positions of the GPS receivers—thisrelative geometry is the UAV attitude—Yaw, Pitch, and Roll.

FIG. 3 is a flow diagram of one embodiment of the steps for comparingGPS carrier phase measurements at each GPS receiver to obtain a precisegeometry of the GPS receivers fixed to the UAV relative to several GPSsatellites. In step S32 the system obtains pseudo-range and carrierphase data from the raw GPS measurements. In step S34 the systemestimates integral component of each receiver-satellite distance. Instep S36 the system estimates the fractional component of eachreceiver-satellite distance. In step S38 the system comparespseudo-range and carrier phase estimated distance components pair-wisebetween GPS receiver/satellite pairs. In step S40 the system calculatesrelative distances between the GPS receivers and each satellite based onthe comparisons. In step S42 the system determines the UAV attitude. Inthis process, error sources such a from the receiver and satelliteclocks are canceled in the relative distance calculation. In oneembodiment, across samples over time, statistical techniques may beapplied to reduce noise in the calculation, such as Kalman Filtering.

In step S28, the “attitude” output of step S26 is used as a known“camera pose” for any video/still cameras mounted to the vehicle. Acrossmultiple video frames, or multiple still images, each pose estimate fromstep S28 provides a precise measure of rotation. The output of step S30is a list of sequential images from the camera with the inter-framerotation between each. It should be noted that the rotation is in threedimensions (3D), capturing each of yaw (a change in compass direction),pitch (nose moving up and down) and roll (rotation along the axis of thevehicular body).

Each attitude measurement may be represented as a 3×3 matrix ofrotation. Consider two attitude matrices, A and B. Also consider that arotation R (another rotation matrix) occurs between A and B such thatR*A=B. Thus, R=B*A{circumflex over ( )}−1. In other words, R=Bright-multiplied by A-inverse.

FIG. 4 is a flow diagram of the method for use the GPS attitude geometryto produce a 3D camera pose rotation matrix of step S28. In steps S44and S46 the UAV attitude for two time points are obtained from step S42.In step S48, each attitude from step steps S44 and Step S46 is encodedas a 3×3 rotation matrix, for the two time points, matrices A and B. Instep S50, the camera rotation R from A to B is solved asR=B*A{circumflex over ( )}−1, that is A is right-matrix-multiplied bythe inverse of A. By properties of rotation matrices, A-inverse may becomputed simply as A-transpose. In step S50, the rotation R, mayoptionally be modified for use in computer vision. For example, R may beconverted to any other representation of 3D rotation, such asQuaternions/Versors, by standard formula.

The camera pose/inter-frame rotation is used as input to fundamentalcomputer vision heuristics. By reducing the computer vision searchspace, the computational complexity is reduced substantially. Computervision heuristic applications include but are not limited to: (1)keypoint detection; (2) keypoint matching; (3) structure from motion;(4) motion tracking, such as optical flow; and (4) blob detection andtracking.

In one embodiment the camera pose is used for visual feature matching.In this scenario a 2D point in an image must be matched to another 2Dpoint in a second image, such that the two 2D points represent the samereal point in 3D space. Such points may be tracked by features, such asthose output by the often-used SIFT feature detector and descriptor.Known rotation can be used to “predict” the location of the feature inthe second image from the first, whereas the rotation corresponds to avisual re-projection of the original image. Any feature detected in thefirst image may be searched for in the second image, using there-projected coordinate as an origin of the search. Instead of searchingarbitrarily throughout the second image, we may first look at thepredicted location, expanding the search boundary from there (e.g., inconcentric circles or progressively-larger bounding boxes). In this way,the search should complete substantially faster than arbitrary matching,where the feature might appear anywhere in the second image. It willalso be faster than searching from the same 2D location in the secondlocation as it appears in the first, and rotation might substantiallymove the correct location in the frame.

FIG. 5 is a flow diagram of one embodiment of the method of using the 3Dcamera pose rotation matrix in computer vision.

In step S28, rotation between two time points is inferred and a 3Drotation matrix for the two points is determined. In step S52, in avideo/photograph stream time-synchronized to GPS measurements, an imagecorresponding to each of the two time points is found. The process mightalso be reversed to find GPS measurements corresponding to the time oftwo desired images. In step S54, from a database or a set of calibrationimages, the fundamental matrix of the camera is obtained, which includesa description of the properties of the lens, such as field of view anddistortional coefficients. Step S56 is combining the fundamental matrixand the matrix of rotation, and the coordinates of original image arere-projected into their predicted location in the next image in stepS58. In step S60, the re-projected coordinate is used as a startingpoint for a search in the second image for the same physicalcharacteristic present in the first image. The search bounds may besystematically expanded around the predicted coordinate. Several searchexpansion heuristics are reasonable, such as concentric circles orprogressively-larger bounding boxes. The appropriate choice is dependenton the computational and memory characteristics of the computer systemon which the search will be run. Due to several factors, such astranslation—horizontal or vertical non-rotation movement of the UAVcraft—and effects of 3D parallax, the re-projection will be imprecise,but will provide a better starting point than arbitrarily selecting apoint. In an optional step, the matching process can be automatedthrough the use of computer vision visual features, such as those fromthe SIFT descriptor. Many other visual feature detector/extractors alsoapply, such as SURF, AKAZE, ORB and BRIEF.

FIG. 6 illustrates a schematic of an example computer or processingsystem that may implement the method for applying GPS UAV attitudeestimation to accelerate computer vision in one embodiment of thepresent disclosure. The computer system is only one example of asuitable processing system and is not intended to suggest any limitationas to the scope of use or functionality of embodiments of themethodology described herein. The processing system shown may beoperational with numerous other general purpose or special purposecomputing system environments or configurations. Examples of well-knowncomputing systems, environments, and/or configurations that may besuitable for use with the processing system shown in FIG. 6 may include,but are not limited to, personal computer systems, server computersystems, thin clients, thick clients, handheld or laptop devices,multiprocessor systems, microprocessor-based systems, set top boxes,programmable consumer electronics, network PCs, minicomputer systems,mainframe computer systems, and distributed cloud computing environmentsthat include any of the above systems or devices, and the like.

The computer system may be described in the general context of computersystem executable instructions, such as program modules, being executedby a computer system. Generally, program modules may include routines,programs, objects, components, logic, data structures, and so on thatperform particular tasks or implement particular abstract data types.The computer system may be practiced in distributed cloud computingenvironments where tasks are performed by remote processing devices thatare linked through a communications network. In a distributed cloudcomputing environment, program modules may be located in both local andremote computer system storage media including memory storage devices.

The components of computer system may include, but are not limited to,one or more processors or processing units 100, a system memory 106, anda bus 104 that couples various system components including system memory106 to processor 100. The processor 100 may include a program module 102that performs the methods described herein. The module 102 may beprogrammed into the integrated circuits of the processor 100, or loadedfrom memory 106, storage device 108, or network 114 or combinationsthereof.

Bus 104 may represent one or more of any of several types of busstructures, including a memory bus or memory controller, a peripheralbus, an accelerated graphics port, and a processor or local bus usingany of a variety of bus architectures. By way of example, and notlimitation, such architectures include Industry Standard Architecture(ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA)bus, Video Electronics Standards Association (VESA) local bus, andPeripheral Component Interconnects (PCI) bus.

Computer system may include a variety of computer system readable media.Such media may be any available media that is accessible by computersystem, and it may include both volatile and non-volatile media,removable and non-removable media.

System memory 106 can include computer system readable media in the formof volatile memory, such as random access memory (RAM) and/or cachememory or others. Computer system may further include otherremovable/non-removable, volatile/non-volatile computer system storagemedia. By way of example only, storage system 108 can be provided forreading from and writing to a non-removable, non-volatile magnetic media(e.g., a “hard drive”). Although not shown, a magnetic disk drive forreading from and writing to a removable, non-volatile magnetic disk(e.g., a “floppy disk”), and an optical disk drive for reading from orwriting to a removable, non-volatile optical disk such as a CD-ROM,DVD-ROM or other optical media can be provided. In such instances, eachcan be connected to bus 104 by one or more data media interfaces.

Computer system may also communicate with one or more external devices116 such as a keyboard, a pointing device, a display 118, etc.; one ormore devices that enable a user to interact with computer system; and/orany devices (e.g., network card, modem, etc.) that enable computersystem to communicate with one or more other computing devices. Suchcommunication can occur via Input/Output (I/O) interfaces 110.

Still yet, computer system can communicate with one or more networks 114such as a local area network (LAN), a general wide area network (WAN),and/or a public network (e.g., the Internet) via network adapter 112. Asdepicted, network adapter 112 communicates with the other components ofcomputer system via bus 104. It should be understood that although notshown, other hardware and/or software components could be used inconjunction with computer system. Examples include, but are not limitedto: microcode, device drivers, redundant processing units, external diskdrive arrays, RAID systems, tape drives, and data archival storagesystems, etc.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include anon-transitory computer readable storage medium (or media) havingcomputer readable program instructions thereon for causing a processorto carry out aspects of the present invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements, if any, in the claims below areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of the present invention has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The embodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

In addition, while preferred embodiments of the present invention havebeen described using specific terms, such description is forillustrative purposes only, and it is to be understood that changes andvariations may be made without departing from the spirit or scope of thefollowing claims.

What is claimed is:
 1. A method for identifying a search space for anobject in images generated from a camera on a UAV having a plurality ofGPS receivers, the method comprising: obtaining measurementsrepresenting distances between each GPS receiver fixed to the UAV andeach GPS satellite in view of the UAV; comparing the measurementspair-wise for each pair of GPS receivers fixed to the UAV and GPSsatellite in view of the UAV to determine relative distancemeasurements; determining an attitude of the UAV based on the relativedistance measurements at each of a plurality of time points; encodingthe attitude of the UAV at a first time point and a second time point asfirst and second 3D rotation matrices, respectively; calculating acamera pose rotation between the first time point and the second timepoint using the first and second 3D camera pose rotation matrices;receiving first image data containing an object from a camera mounted onthe UAV taken at the first time point and receiving second image datafrom the camera mounted on the UAV taken at the second time point; andanalyzing the first and second image data received from the UAV at thefirst and second time points, respectively, and projecting the firstimage data onto the second image data using the calculated camera poserotation to identify a search space for the object in the second imagedata based on the image projection.
 2. The method of claim 1, furthercomprising receiving GPS signals from each GPS satellite in view of theUAV, the GPS signals comprising respective pn codes and carrierfrequencies; obtaining carrier phase and pseudo-range measurements foreach GPS receiver fixed to the UAV based on the respective pn codes andcarrier frequencies, the pseudo-range and carrier phase datameasurements representing the distance between each GPS receiver fixedto the UAV and each GPS satellite in view of the UAV; and comparing theGPS carrier phase and pseudo-range measurements pair-wise for each pairof GPS receivers fixed to the UAV and GPS satellite in view of the UAVto determine relative distance measurements.
 3. The method of claim 1,wherein determining the 3D camera pose rotation matrix based on theattitude of the UAV comprises the steps of: determining a first attitudeof the UAV at a first time point; determining a second attitude of theUAV at a second time point; encoding the first attitude of the UAV as afirst 3×3 rotation matrix and encoding the second attitude of the UAV asa second 3×3 rotation matrix; and calculating a rotation of the camerabetween the first and second time points by multiplying the firstrotation matrix by the inverse of the second rotation matrix andencoding the results as the 3D camera pose rotation matrix.
 4. Themethod of claim 2, wherein determining the carrier phase andpseudo-range measurements comprises estimating an integral component ofthe distance between each GPS receiver and each GPS satellite using thepseudo-range data and estimating a fractional component of the distancebetween each GPS receiver and each GPS satellite using the carrier phasedata.
 5. The method of claim 4 wherein comparing the GPS carrier phaseand pseudo-range measurements comprises comparing the pseudo-range andcarrier phase estimated distance components pair-wise between the GPSreceiver and satellite pairs.
 6. The method of claim 5, whereindetermining an attitude of the UAV comprises calculating relativedistances between the GPS receivers and each satellite based on thecomparisons and determining the attitude of the UAV based on therelative distances between GPS receivers and satellites.
 7. The methodof claim 1, further comprising: predicting coordinates of the object inthe image data at the second time point based on the estimated camerapose rotation; locating coordinates of an image corresponding to thefirst and second time points in a first video or photograph streamtime-synchronized to the GPS signals; obtaining a camera matrix definingproperties of the camera; combining the camera matrix and the 3D camerapose rotation matrix to determine predicted coordinates of the image ina second video or photograph stream time; projecting the predictedcoordinates of the image into the second video or photograph streamtime; and using the projected coordinates as a starting point for asearch in the second video or photograph stream for an image having thesame physical characteristics of the image.
 8. A non-transitory articleof manufacture tangibly embodying computer readable instructions, whichwhen implemented, cause a computer to perform the steps of a method foridentifying a search space for an object in images generated from acamera on a UAV having a plurality of GPS receivers, comprising;obtaining measurements representing distances between each GPS receiverfixed to the UAV and each GPS satellite in view of the UAV; comparingthe measurements pair-wise for each pair of GPS receivers fixed to theUAV and GPS satellite in view of the UAV to determine relative distancemeasurements; determining an attitude of the UAV based on the relativedistance measurements at each of a plurality of time points; encodingthe attitude of the UAV at a first time point and a second time point asfirst and second 3D rotation matrices, respectively; calculating acamera pose rotation between the first time point and the second timepoint using the first and second 3D camera pose rotation matrices;receiving first image data containing an object from a camera mounted onthe UAV taken at the first time point and receiving second image datafrom the camera mounted on the UAV taken at the second time point; andanalyzing the first and second image data received from the UAV at thefirst and second time points, respectively, and projecting the firstimage data onto the second image data using the calculated camera poserotation to identify a search space for the object in the second imagedata based on the image projection.
 9. The non-transitory article ofmanufacture of claim 8, further comprising receiving GPS signals fromeach GPS satellite in view of the UAV, the GPS signals comprisingrespective pn codes and carrier frequencies; obtaining carrier phase andpseudo-range measurements for each GPS receiver fixed to the UAV basedon the respective pn codes and carrier frequencies, the pseudo-range andcarrier phase data measurements representing the distance between eachGPS receiver fixed to the UAV and each GPS satellite in view of the UAV;and comparing the GPS carrier phase and pseudo-range measurementspair-wise for each pair of GPS receivers fixed to the UAV and GPSsatellite in view of the UAV to determine relative distancemeasurements.
 10. The non-transitory article of manufacture of claim 8,wherein determining the 3D camera pose rotation matrix based on theattitude of the UAV comprises the steps of: determining a first attitudeof the UAV at a first time point; determining a second attitude of theUAV at a second time point; encoding the first attitude of the UAV as afirst 3×3 rotation matrix and encoding the second attitude of the UAV asa second 3×3 rotation matrix; and calculating a rotation of the camerabetween the first and second time points by multiplying the firstrotation matrix by the inverse of the second rotation matrix andencoding the results as the 3D camera pose rotation matrix.
 11. Thenon-transitory article of manufacture of claim 9, wherein determiningthe carrier phase and pseudo-range measurements comprises estimating anintegral component of the distance between each GPS receiver and eachGPS satellite using the pseudo-range data and estimating a fractionalcomponent of the distance between each GPS receiver and each GPSsatellite using the carrier phase data.
 12. The non-transitory articleof manufacture of claim 11, wherein comparing the GPS carrier phase andpseudo-range measurements comprises comparing the pseudo-range andcarrier phase estimated distance components pair-wise between the GPSreceiver and satellite airs.
 13. The non-transitory article ofmanufacture of claim 12, wherein determining an attitude of the UAVcomprises calculating relative distances between the GPS receivers andeach satellite based on the comparisons and determining the attitude ofthe UAV based on the relative distances between GPS receivers andsatellites.
 14. The non-transitory article of manufacture of claim 13,further comprising: predicting coordinates of the object in the imagedata at the second time point based on the estimated camera poserotation; locating coordinates of an image corresponding to the firstand second time points in a first video or photograph streamtime-synchronized to the GPS signals; obtaining a camera matrix definingproperties of the camera; combining the camera matrix and the 3D camerapose rotation matrix to determine predicted coordinates of the image ina second video or photograph stream time; projecting the predictedcoordinates of the image into the second video or photograph streamtime; and using the projected coordinates as a starting point for asearch in the second video or photograph stream for an image having thesame physical characteristics of the image.
 15. A computer system foridentifying a search space for an object in images generated from acamera on a UAV having a plurality of GPS receivers comprising: one ormore computer processors; one or more non-transitory computer-readablestorage media; program instructions, stored on the one or morenon-transitory computer-readable storage media, which when implementedby the one or more processors, cause the computer system to perform thesteps of: obtaining measurements representing distances between each GPSreceiver fixed to the UAV and each GPS satellite in view of the UAV;comparing the measurements pair-wise for each pair of GPS receiversfixed to the UAV and GPS satellite in view of the UAV to determinerelative distance measurements; determining an attitude of the UAV basedon the relative distance measurements at each of a plurality of timepoints; encoding the attitude of the UAV at a first time point and asecond time point as first and second 3D rotation matrices,respectively; calculating a camera pose rotation between the first timepoint and the second time point using the first and second 3D camerapose rotation matrices; receiving first image data containing an objectfrom a camera mounted on the UAV taken at the first time point andreceiving second image data from the camera mounted on the UAV taken atthe second time point; and analyzing the first and second image datareceived from the UAV at the first and second time points, respectively,and projecting the first image data onto the second image data using thecalculated camera pose rotation to identify a search space for theobject in the second image data based on the image projection.
 16. Thecomputer system of claim 15, further comprising receiving GPS signalsfrom each GPS satellite in view of the UAV, the GPS signals comprisingrespective pn codes and carrier frequencies; obtaining carrier phase andpseudo-range measurements for each GPS receiver fixed to the UAV basedon the respective pn codes and carrier frequencies, the pseudo-range andcarrier phase data measurements representing the distance between eachGPS receiver fixed to the UAV and each GPS satellite in view of the UAV;and comparing the GPS carrier phase and pseudo-range measurementspair-wise for each pair of GPS receivers fixed to the UAV and GPSsatellite in view of the UAV to determine relative distancemeasurements.
 17. The computer system of claim 15, wherein determiningthe 3D camera pose rotation matrix based on the attitude of the UAVcomprises the steps of: determining a first attitude of the UAV at afirst time point; determining a second attitude of the UAV at a secondtime point; encoding the first attitude of the UAV as a first 3×3rotation matrix and encoding the second attitude of the UAV as a second3×3 rotation matrix; and calculating a rotation of the camera betweenthe first and second time points by multiplying the first rotationmatrix by the inverse of the second rotation matrix and encoding theresults as the 3D camera pose rotation matrix.
 18. The computer systemof claim 16, wherein determining the carrier phase and pseudo-rangemeasurements comprises estimating an integral component of the distancebetween each GPS receiver and each GPS satellite using the pseudo-rangedata and estimating a fractional component of the distance between eachGPS receiver and each GPS satellite using the carrier phase data. 19.The computer system of claim 18, wherein comparing the GPS carrier phaseand pseudo-range measurements comprises comparing the pseudo-range andcarrier phase estimated distance components pair-wise between the GPSreceiver and satellite pairs.
 20. The computer system of claim 19,wherein determining an attitude of the UAV comprises calculatingrelative distances between the GPS receivers and each satellite based onthe comparisons and determining the attitude of the UAV based on therelative distances between GPS receivers and satellites.
 21. Thecomputer system of claim 15, further comprising: predicting coordinatesof the object in the image data at the second time point based on theestimated camera pose rotation; locating coordinates of an imagecorresponding to the first and second time points in a first video orphotograph stream time-synchronized to the GPS signals; obtaining acamera matrix defining properties of the camera; combining the cameramatrix and the 3D camera pose rotation matrix to determine predictedcoordinates of the image in a second video or photograph stream;projecting the predicted coordinates of the image into the second videoor photograph stream time; and using the projected coordinates as astarting point for a search in the second video or photograph stream foran image having the same physical characteristics of the image.